AGA Report No 5 Natural Gas Energy
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AGA Report No. 5 Natural Gas Energy Measurement
Prepared by Transmission Measurement Committee March 2009 2009
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AGA Report No. 5
Natural Gas Energy Measurement Prepared by
Transmission Measurement Committee
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Copyright 2009 © American Gas Association All Rights Reserved
Catalog # XQ0901
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DISCLAIMER AND COPYRIGHT The American Gas Association’s (AGA) Operations and Engineering Section provides a forum for industry experts to bring collective knowledge together to improve the state of the art in the areas of operating, engineering and technological aspects of producing, gathering, transporting, storing, distributing, measuring and utilizing natural gas. Through its publications, of which this is one, AGA provides for the exchange of information within the gas industry and scientific, trade and governmental organizations. Each publication is prepared or sponsored by an AGA Operations and Engineering Section technical committee. While AGA may administer the process, neither AGA nor the technical committee independently tests, evaluates or verifies the accuracy of any information or the soundness of any judgments contained therein. ` , , ` ` ` , , , , ` ` ` ` ` ` , , ` , , ` , ` , , ` -
AGA disclaims liability for any personal injury, property or other damages of any nature whatsoever, whether special, indirect, consequential or compensatory, directly or indirectly resulting from the publication, use of or reliance on AGA publications. AGA makes no guaranty or warranty as to the accuracy and completeness of any information published therein. The information contained therein is provided on an “as is” basis and AGA makes no representations or warranties including any expressed or implied warranty of merchantability or fitness for a particular purpose. In issuing and making this document available, AGA is not undertaking to render professional or other services for or on behalf of any person or entity. Nor is AGA undertaking to perform any duty owed by any person or entity to someone else. Anyone using this document should rely on his or her own independent judgment or, as appropriate, seek the advice of a competent professional in determining determining the exercise of reasonable reasonable care in any given circumstanc circumstances. es. AGA has no power, nor does it undertake, to police or enforce compliance with the contents of this document. Nor does AGA list, certify, test or inspect products, designs or installations for compliance with this document. Any certification or other statement of compliance is solely the responsibility responsibilit y of the certifier or maker of the statement. AGA does not take any position with respect to the validity of any patent rights asserted in connection with any items that are mentioned in or are the subject of AGA publications, and AGA disclaims liability for the infringement of any patent resulting from the use of or reliance on its publications. Users of these publications are expressly advised that determination of the validity of any such patent rights, and the risk of infringement of such rights, is entirely their own responsibility. Users of this publication should consult applicable federal, state and local laws and regulations. AGA does not, through its publications intend to urge action that is not in compliance with applicable laws, and its publications may not be construed as doing so. This report is the cumulative result of years of experience of many individuals and organizations acquainted with the measurement of natural gas. However, changes to this report may become necessary from time to time. If changes to this report are believed appropriate by any manufacturer, individual or organization, such suggested changes should be communicated to AGA by completing the last page of this report titled, “Form for Proposal on AGA Report No. 5” and sending it to: Operations & Engineering Section, American Gas Association, 400 th North Capitol Street, NW, 4 Floor, Washington, DC 20001, U.S.A. Copyright 2009, American Gas Association, All Rights Reserved.
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ACKNOWLEDGEMENTS AGA Report No. 5, Natural Gas Energy Measurement, was revised by a Task Group of the American Gas Association’s Transmission Measurement Committee under the joint chairmanship of Warren Peterson with TransCanada Pipelines Limited and and James Witte with El Paso Corporation with substantial contributions from Eric Lemmon with the the National Institute of Standards and Technology. Individuals who made considerable contributions to the revision of this document are: Kenneth Starling, Starling Associates, Inc. Paul LaNasa, CPL & Associates Paul Kizer, Formerly with ABB, Inc. Other individuals who also contributed to the revision of the document are: Stephen Hall, TransCanada Pipelines Limited Thanh Phan, Spectra Energy Corp. Joe Bronner, Pacific Gas and Electric Company Hank Poellnitz, Southern Natural Gas Company Eric Kelner, Formerly with Southwest Research Institute Ed Bowles, Southwest Research Institute Mark Maxwell, Instromet, Inc. Frank Brown, Consultant
AGA acknowledges the contributions of the above individuals and thanks them for their time and effort in getting this document revised.
Christina Sames Vice President Operations and Engineering
Ali Quraishi, Staff Executive Engineering Services Director Operations and Engineering
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FOREWORD
This report is published to foster consensus among parties conducting energy-based measurement of natural gas. The report addresses methods, assumptions and criteria relevant to the determination of heating value and heat energy. Gas property measurement has a history of continual refinement. A goal of this report is to provide stabilizing influence through the stewardship of the Transmission Measurement Committee of the American Gas Association. This revision was triggered by technology advancement and heightened industry attention to gas quality issues. This version of AGA Report No. 5 supersedes all prior versions of this document. Users of previous editions are advised advised to upgrade to thi thiss edition. Programs in Excel Spreadsheet for AGA 5 related calculations including heating values both in Imperial and SI units are provided with this report.
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TABLE OF CONTENTS DISCLAIMER AND COPYRIGHT................. .................................... ..................................... ..................................... .................................... ................. III ACKNOWLEDGEMENTS ........................................................................................................ IV FOREWORD ................................................................................................................................. V TABLE OF CONTENTS ............................................................................................................ VI 1. SCOPE OF APPLICATION ...................................................................................................1 ...................................................................................................1 1.1 General ......................................................................................................................... 1 1.2 Range Of Application .................................................................................................. 1 1.2.1 Inclusion Criteria Criteria for Fuel Gas Mixtures................................... ................. ..................................... ............................. .......... 1 1.3 Range of Gas Mixture Constituents ............................................................................. 2 1.3.1 Concentration of Gas Constituents.......................................................................... Constituents.......................................................................... 2 1.3.2 Directly Supported Constituents Constituents..................................... ................... ..................................... ..................................... ...................... .... 2 1.3.3 Other Constituents ................................................................................................... 3 1.3.4 Grouped Constituents .............................................................................................. 3 1.4 Other Composition-Dependent Composition-Dependent Gas Properties ................................... ................. .................................... ......................... ....... 4 1.5 Range of Contract Base Pressures and Contract Base Temperatures .......................... ................ .......... 4 1.6 Compounds in the Liquid State.................................................................................... 4 2. DEFINITIONS AND BACKGROUND ................................... ................. .................................... .................................... ............................ .......... 5 2.1 British Thermal Unit (Btu)........................................................................................... 5
2.2 .......................................................................................................................... 5 2.3 Calorie Combustion .................................................................................................................. 5 2.4 Combustion Reference Temperature ........................................................................... 7 2.5 Contract Base Conditions ............................................................................................ 8 2.6 Dekatherm .................................................................................................................... 8 2.7 Dry Gas ........................................................................................................................ 8 2.8 Higher Heating Value (HHV), also known as Gross Heating Value (GHV) ............... 8 2.9 Ideal Gas ...................................................................................................................... 8 2.10 Motor Octane Number (MON) .................................................................................... 9 2.11 Methane Number (MN) ............................................................................................... 9 2.12 Natural Gas Energy Measurement ................. ................................... ..................................... ..................................... ......................... ....... 9 2.13 Lower Heating Value (LHV), also known as Net Heating Value (NHV) ................... 9 2.14 Real Gas ....................................................................................................................... 9 2.15 Relative Density and Specific Gravity ....................................................................... 10
2.16 Sensible Heat ............................................................................................................. 10 2.17 Therm ......................................................................................................................... 10 2.18 Water Dew Point ........................................................................................................ 10 2.19 Water-Saturated and Partially Water-Saturated Gases .............................................. 10 2.20 Wobbe Number (WN), also known as Wobbe Index (WI)................. .................................... ....................... .... 11 3. BASIS FOR CUSTODY TRANSFER .................................... ................. ..................................... ..................................... ........................... ........ 12 3.1 Specification of Energy ............................................................................................. 12 3.2 Specification of Heating Value .................................................................................. 12 3.3 Higher (Gross) Versus Lower (Net) Heating Value .................................................. 12 3.4 Dry Versus Saturated Heating Value ......................................................................... 12 3.5 Energy Derived from Volumetric Measurements ................................... ................. ..................................... ................... 13 3.6 Energy Derived from Mass Measurements...................................... ................... ...................................... .......................... ....... 13 3.7 Sampling and Off-line Analysis................................................................................. Analysis ................................................................................. 13 3.8 Compressibility Factor ............................................................................................... 13 3.9 Enthalpy ..................................................................................................................... 14 3.10 Acc Accoun ountin ting g for the Presenc Presencee of Water Water ......................................... ........................ ................................... .................................. ................ 14 vi --`,,```,,,,````-`-`,,`,,`,`,,`---
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4. UNCERTAINTY .................................................................................................................... 16 4.1 Acceptance Criteria .................................................................................................... 16 5. HEATING VALUE DETERMINATION METHODS .................................... .................. .................................... .................. 17 5.1 Heating Value from Gas Composition ....................................................................... 17 5.1.1 General Requirements ........................................................................................... 17 5.1.2 Gas Chromatography ............................................................................................ 17 5.1.3 Mass Spectrometry ................... ..................................... .................................... ..................................... ..................................... ...................... .... 17 5.2 Heating Value Measurement...................................................................................... 17 5.2.1 General Requirements ........................................................................................... 17 5.2.2 Calorimeter............................................................................................................ 17 5.2.3 Fuel/Air Titration .................................................................................................. 18 5.3 Heating Value from Inferential (Correlative) Methods ............................................. 18 6. REFERENCES....................................................................................................................... 19 APPENDIX A ............................................................................................................................ A-1 Pre-Calculated Tables of Ideal Gas Gross Heating Value (Volumetric Basis) ................. A-2 Pre-Calculated Tables of Ideal Gas Gross Heating Value (Mass Basis) ........................... ..................... ...... A-4 Example Calculation of Volumetric Heating Value (Imperial units) .................. ................................ .............. A-6 Example Calculation of Volumetric Heating Value (SI Units) .................................... ................. ........................ ..... A-8 Standard Enthalpies of Formation ................................................................................... A-10 Stoichiometric Coefficients ............................................................................................. A-11 Balanced Combustion Reaction Equations for Common Hydrocarbons ........................ A-12 Ideal Gas Molar Heating Values at 298.15 K ................................................................. A-12 Enthalpy of Vaporization of Water ................................................................................. A-13 Enthalpy Adjustment ....................................................................................................... A-13 Equation Constants for the Ideal Gas Heat Capacity Correlation ................................... .................. ................. A-15 Calculation of Summations Factors ................................................................................ A-16 Equation Constants for 2nd Virial Coefficients .................. .................................... ..................................... ............................ ......... A-18 Summation Factors at Common Reference Temperatures ..................................... .................. ............................ ......... A-19 Molar Masses .................................................................................................................. A-21 Table of H/C (Hydrogen to Carbon) Ratios .................................................................... A-22 Example Process for Supporting Additional Compounds................. ................................... .............................. ............ A-23 Calculating Natural Gas Relative Density and the Compressibility of Air ..................... .................. ... A-26 Estimation of Water Content from Dew Point Measurements ................. ................................... ....................... ..... A-28 Dew Point Temperature Versus Water Content in Natural Gas ................................... ................ ...................... ... A-29 APPENDIX B.................................. ................ ................................... ................................... ................................... ................................... ...................................... ...................... ..B-1 FORM FOR PROPOSALS ON AGA REPORT NO. 5, MARCH 2009 ............................... ................ ............... B-1
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1. Scope of Application 1.1
General
This report applies specifically to energy-based custody transfer measurement of natural gas. It may or may not be suitable to other applications, as determined by the user. Heating value measurement is used in tandem with volume flow or mass flow measurement, the use of which is guided by other standards. documents. This report is not intended to supersede, extend or duplicate thereports contentand of industry flow measurement For ease of use, this report supports two approaches to estimating heating value from composition: simplified ‘table look-up’ or full calculation. The approaches are functionally equivalent because the look-up tables were produced with the calculation methods. The tables A.1.1 and A.1.2 provide pre-calculated heating values of common gas constituents for a range of common reference conditions. The detailed methods and data elsewhere in this report are primarily for traceability. Report No. 5 differs in scope from other documents concerning energy measurement. In addition to technical data and formulas, this report recommends performance criteria. The physical property data reproduced in this report were drawn from widely-accepted industry sources, including NIST[1] and CODATA[12]. Results obtained using this report will agree closely with results from methods sharing its lineage. In keeping with gas industry practice, this report supports both SI and Imperial units of measure. 1.2
Range Of Application
This report is focussed on methods for predicting the heat energy resulting from complete combustion of commercially acceptable natural gas. 1.2.1 Inclusion Criteria for for Fuel Gas Mixtures This report is valid only for fuel gas mixtures meeting the following criteria: • the fuel must be in the gas phase at the specified reference conditions. • air/fuel mixtures must be capable of ignition followed by self-sustaining, exothermic combustion reactions. • hydrocarbon combustion reactions must reach stoichiometric completion, resulting in product water and carbon dioxide. • trace products of combustion, such as NOx and CO, are negligible in the context of heat production in the scope of this report are: Not in
• • •
combustion characteristics such as flame geometry and air/fuel ratio determination of emissions or the products of incomplete combustion natural Gas Interchangeability indices, other than Wobbe Number, Methane Number (MN) and Motor Octane Number (MON) (MON)
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1.3
Range of Gas Mixture Constituents
1.3.1 Concentration of Gas Constituents The maximum proportion or concentration of constituents within a mixture is limited only by the criteria given in section 1.2.1. 1.3.2 Directly Directly Supported Constituents Constituents The gas mixture constituents directly supported by this report are:
• •
Methane Ethane
•
Propane
•
Isobutane (iC4) and Normal Butane (nC5)
•
Isopentane (iC5) and Normal Pentane (nC5)
•
Normal Hexane (nC6)
•
Normal Heptane (nC7)
•
Normal Octane (nC8)
•
Normal Nonane (nC9)
• •
Normal Decane (nC10)
•
Hydrogen Sulfide (H2S)
•
Oxygen (O2)
•
Water (H2O)
•
Carbon Dioxide (CO2)
•
Carbon Monoxide (CO)
•
Nitrogen (N2)
•
Helium (He)
• •
Argon (Ar) 2,2-Dimethyl Propane
•
2-Methyl Pentane
•
3-Methyl Pentane
•
2,2-Dimethyl Butane
•
2,3-Dimethyl Butane
•
Ethylene
•
Propylene
•
Methyl Alcohol
Hydrogen (H2)
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1.3.3 Other Constituents The methods of this report may also be applicable to other potential gas constituents if the following parameters are available:
•
compound molar mass
•
enthalpy of formation at 25 °C (77 °F)
•
second virial coefficient or summation factor at the temperature of interest
• •
stoichiometric coefficients calculation parameters for ideal gas heat capacity
1.3.4 Grouped Constituents In the context of energy measurement, it is possible to characterize some compounds as constituents of a group rather than as individual constituent. A group of compounds may be thoug thought ht of as a ‘‘ps pseud eudo-c o-com ompou pound’ nd’ who whose se proper propertie tiess aare re infer inferred red fro from m tthos hosee of of iits ts member members. s. For example, the ‘pseudo-compound’ C6+ represents the sum of all hydrocarbons whose carbon number is 6 and higher. Typically, C6+ represents pre-determined proportions of nC6, nC nC7 and nC8. A number of ‘default’ proportions are widely used but none are mandated. The following two examples illustrate the sensitivity of heating value to assumed proportions within within C6+. The ‘Amarillo’ example gas listed in AGA Report No. 8 (2 nd edition) includes 0.0393 mole percent of normal C6. The calculated gross heating value of the mixture is 1034.8 Btu per cubic foot at 14.73 psia and 60 °F. For comparison, assume the mixture contains C6+ with 60/30/10 proportions. Upon recalculation, the heating value is higher by 0.015% (1035.0 Btu per cubic foot). In this scenario, heating value is relatively insensitive to the assumed composition of C6+. Consider a contrasting example, where a natural gas mixture consists of: • 84 mole percent methane
•
5.0 mole percent nitrogen
•
6.0 mole percent ethane
•
3.0 mole percent propane
•
1.0 mole percent normal butane
•
0.5 mole percent normal pentane
•
0.5 mole percent normal hexane
The calculated gross heating value of this mixture is 1112.1 Btu per cubic foot at 14.73 psia and 60 °F. Assume the hexane fraction is, instead, C6+ with 60/30/10 proportions. The re-calculated heating value is higher by 0.17% (1114.0 Btu per cubic foot). The influence of the C6+ breakdown in this example is notably larger than that of the first example.
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1.4
Other Composition-Dependent Gas Properties
Several types of measurement-related calculations rely on gas composition, including hydrocarbon dew point, density, sound speed and heat capacity. Some of these calculations are more sensitive than others to error in gas composition measurement. For instance, calculations of hydrocarbon dew point tend to be very sensitive to the concentration of heavier hydrocarbons. Do not assume that the heating value measurement uncertainty will be representative of the uncertainty for other properties. 1.5
Range of Contract Base Pressures and Contract Base Temperatures
The methods in this report are suitable for the following conditions: Pressure: Temperature:
P < 16 psia 32 °F < T < 77 °F
P < 112 kPa 0 °C < T < 25 °C
The methods of this report address the influence of pressure, temperature and compressibility on gas density. Over the range of contract base conditions given in this report, gas enthalpy is compensated for the influence of temperature. For reasons given in section 3.9, enthalpy is not compensated for pressure. 1.6
Compounds in the Liquid State
For certain gas industry transactions, a theoretical gas heating value may be associated with compounds measured in their liquid state. state. Note that gas-state heating value is not the same as liquid-state heating value, due to the enthalpy of vaporization and the effects of gas compressibility. For gas measurement applications associated with condensates, NGL or LNG, the heating value of such quantities shall be stated in terms of their heating value in the gas state and not in terms of their heating value in the liquid state. Correspondingly, heating value may be reported on a mass basis or an ideal gas volume basis. A potential for error also arises from gas/liquid volume conversions, due to the difference between real gas and ideal gas behaviour. To avoid potential error, perform gas/liquid conversions based on mass rather than volume. If volume-based conversions are required, consult applicable industry standards, such as GPA 8173.
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2. Definitions and Background 2.1
British Thermal Unit (Btu)
The International Table Btu, or BtuIT, is a unit of energy defined in terms of the International Table calorie and the SI unit of energy, the joule (J). For the purpose of custody transfer measurement, 1 BtuIT = 1055.05585262 J. A rounded version (1055.056) may be acceptable. The BtuIT is defined in terms of its relationship to the joule and the kilogram. 1 BtuIT per pound mass
=
2326 kJ/kg (exact)
1 pound mass
=
0.45359237 kg (exact)
1 BtuIT
=
2326 x 0.45359237 = 1055.05585262 J
The International Table Btu was adopted in the 1977 revision of ASTM D 1826-77 “Test Method for Calorific Value of Natural Gas Ranges by Continuous recording Calorimeter”[14], and referenced in subsequent AGA publications. Prior to the publication of AGA Engineering Technical Note M-92-2-1[13], the version of the Btu supported by the AGA Transmission Measurement Committee was the Btu (58.5-59.5). Traditionally, Btu of was defined terms the°F.heat required to raise was the temperature of the a pound water from in 58.5 °F toof 59.5 The energy temperature specification required because the heat capacity of water varies with temperature. A potential bias exists betwee bet ween n part parties ies whose whose Btu is defin defined ed di diffe fferen rently tly (fo (forr exa exampl mple, e, Btu(58.5-59.5) versus Btu(60-61)). 2.2
Calorie
A calorie is a unit of measurement of energy. In most fields, the calorie has been replaced by the joule, the SI derived unit of energy. One calorie is approximately the heat energy required to raise the temperature of 1 gram of water by 1 degree Celsius. Five variations of the calorie exist, due to differences in their associated reference temperatures. The two variants associated with natural gas properties are the International Table calorie (1 calIT = 4.1868 J) and the thermo-chemical calorie (1 cal(th) = 4.184 J). 2.3
Combustion
Combustion is a rapid sequence of chemical reactions between fuel and oxidant, accompanied by heat and light. During combustion of natural gas, hydrocarbon compounds react with oxygen to yield carbon dioxide and water. The ratio of oxygen molecules to fuel molecules is proportional to the carbon number or the number of carbon atoms in the fuel molecule. The higher the carbon number, the greater number of oxygen molecules required to complete the reaction.
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The quantitative relationship between reactants and products in chemical reactions is called stoichiometry. The stoichiometric equation for balancing oxidation reactions involving hydrocarbons is:
4C n H (2n+ 2 ) + (6n + 2) O2
⇒ 4nCO2 + (4n + 4) H 2O + energy
(1)
Where: n
=
number of carbon atoms in the hydrocarbon molecule
(2n+2) C n H (2n+2)
=
O2
=
hydrocarbon molecule oxygen molecule
CO2
=
carbon dioxide molecule
H 2O
=
water molecule
Balanced equations for several hydrocarbons are given in the Table A.7.1. Other combustible compounds may also be present in the gas mixture. The respective oxidation reaction equations for H2S, H2 and CO are given by:
2 H 2 S + 3O2
⇒ 2SO2 + 2 H 2O + energy
2 H 2 + O2
⇒ 2 H 2O + energy 2CO + O 2 ⇒ 2CO2 + energy
(2) (3) (4)
Some compounds that may be found in natural gas, such as nitrogen, carbon dioxide, oxygen, helium and argon are called ‘spectators’ to combustion because they do not oxidize and act only as diluents in a fuel gas composition. There is a special case when water vapor is present in the fuel. While not a participant in combustion,, water contributes energy if it is condensed from vapor to liquid in the exhaust stream. combustion If insufficient oxygen is available for reaction with fuel, incomplete combustion may yield compounds such as CO. In the following example equation for the oxidation of methane, the reaction is exothermic.
CH 4 + 2O2
⇒ CO2 + 2 H 2O
(5)
That is, the enthalpy of formation for the CH 4 molecules prior to reaction is greater than the enthalpies of formation for CO2 and H2O yielded by the reaction. Enthalpies are often stated on a molar basis, in units of kilojoules per mole.
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The energy available from combustion is directly related, then, to the enthalpies of formation and the stoichiometric coefficients given in tables A.5.1 and A.6.1
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The molar ideal gross heating value of the ith constituent at the reference condition T h and Ph is given by the following relation:
HN (T h , Ph ) = − o i
NC
∑
(6)
SC i ,k HF k (T h , Ph ) o
k =1
Where: molar ideal gas gross heating value of the ith constituent at T h , Ph
HN io (T h , Ph ) = =
stoichiometric coefficient of constituent k for combustion of ith
HF k o (T h , Ph ) =
constituent molar ideal gas enthalpy of formation of constituent k at at T h,
SC i ,k
T h
=
reference temperature for heating value
Ph
=
reference pressure for heating value
The molar ideal gross heating value of a dry gas mixture is related to the composition of the mixture by the following relation:
HN (T h , Ph ) = o
(7)
NC
∑
xi HN io (T h , Ph )
i =1
Where:
HN o (T h , Ph )
=
molar ideal gas gross heating value of the gas m mixture ixture at T h , Ph
HN io (T h , Ph )
=
molar ideal gas gross heating value of the ith constituent at T h , Ph
xi
=
mole fraction of ith constituent in gas mixture
NC
=
number of combustible constituents in gas mixture
Natural gas heating value is commonly expressed on a volume basis. The volumetric heating value is obtained by multiplying molar heating value by molar density. o HV (T h , Ph ) = HN (T h , Ph )ρ (T h , Ph )
(8)
Where: ` , , ` ` ` , , , , ` ` ` ` ` ` , , ` , , ` , ` , , ` -
=
volumetric gas gross heating value of the gas mixture at T h , Ph
HN o (T h , Ph )
=
molar ideal gas gross heating value of the gas mixture at T h , Ph
(T h , Ph )
=
molar gas density at T h , Ph
HV (T h , Ph ) ρ
Expressed in terms of compressibility, volumetric heating value is the ideal gas volumetric heating value divided by the compressibility factor Z , at reference conditions.
(T h , Ph ) HV
(9)
0
HV (T h , Ph ) =
2.4
Z mix (T h , Ph )
Combustion Reference Temperature
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2.5
Contract Base Conditions
Arbitrarily defined pressure and temperature conditions are used for quantifying gas volume or volumetric heating value. This is industry’s approach for quantifying products whose properties vary with operating conditions. Contract base conditions vary somewhat across industry, which may require users to implement mathematical conversions. When energy is reported as the product of volume and volumetric heating value, it is imperative that the base conditions for both parameters be identical. 2.6
Dekatherm
A dekatherm is a unit of energy, 1 dekatherm = 10 therms = 1,000,000 BtuIT 2.7
(10)
Dry Gas
For the purpose of this report, a dry gas is one whose constituent water vapor is less than 112 mg/m3 or 7 lbs mass (lbm) per million standard cubic feet. For energy calculations involving dry natural gas, the concentration of water is less than 0.01 mole percent and therefore assumed to be zero. 2.8
Higher Heating Value (HHV), also known as Gross Heating Value (GHV)
The heat energy generated by complete stoichiometric combustion of a defined quantity of reactants, where the products of combustion are returned to the temperature of the reactants and the water produced by combustion is condensed to the liquid state. Water vapor accompanying unburned fuel is assumed to have condensed in the exhaust gas stream. Water vapor accompanying combustion air is not considered. 2.9
Ideal Gas
An ideal gas is one that observes the Ideal Gas Law equation, PV = nRT
(11)
Where: P = V = n = R = T =
gas pressure gas volume the number of moles of substance the molar gas constant thermodynamic temperature
Gas measurement calculations address the fact that all gases depart, at least somewhat, from the ideal gas law. See also Real Gas, Section 2.14.
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2.10 Motor Octane Number (MON) Motor Octane Number is a numerical rating of the resistance of a motor fuel to knock, scaled for compatibility with gasoline octane ratings. One of the methods for estimating MON for natural gas mixtures is used by the California Air Resources Board (CARB). The equation for the CARB method, as a s documented in SAE paper 922359 [19], is: 2
⎛ H ⎞ ⎛ H ⎞ MON = −406.14 + 508.04 × − 173.55 × ⎜ ⎟ + 20.17 × ⎜ ⎟ C ⎝ C ⎠ ⎝ C ⎠ H
3
(12)
Where: H/C is the ratio of hydrogen atoms to carbon atoms in the reactive hydrocarbons present in the fuel mixture, excluding the carbon atoms in CO2 that may be present. This equation is used when H/C > 2.5 and the sum of the non-hydrocarbon constituents constituents is less than 5 mole percent. Another method for estimating MON is the Linear Coefficient Relation: MON =137.78× X
C1
+ 29.948× X C 2 −18.193× X C 3 −167.062× X C4 +181.233× X CO 2 + 26.994× X N 2
(13)
2.11 Methane Number (MN) Methane Number is a numerical rating of the resistance of a natural gas motor fuel to knock. Methane Number is related approximately to MON by the following equation:
− 119 .1 MN = 1.624 × MON
(14)
2.12 Natural Gas Energy Measurement Measurement of natural gas quantities defined in terms of potential to release energy when combusted. 2.13 Lower Heating Value (LHV), also known as Net Heating Value (NHV) The heat energy generated by complete stoichiometric combustion of a defined quantity of reactants, theby products of combustion the temperature of the reactants and water where produced combustion remains inare thereturned gaseous to state. 2.14 Real Gas A real gas is one whose behaviour departs from the Ideal Gas Law. Compressibility factor ( Z Z ) is a parameter commonly used to symbolize this departure. For calculations involving real gas, the resulting equation is PV = nRTZ . Where: P = V = n = R =
pressure volume number of moles moles of substance substance molar gas constant
T = thermodynamic temperature Z = compressibility factor
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For the purpose of this report, pressure changes are recognized for gas density but ignored for enthalpy departure. Heating values derived from this report are, in the strictest sense: Heating Value = Ideal Gas Molar Heating Value x Real Gas Molar Density
(15) (15 )
2.15 Relative Density and Specific Gravity Relative density is the ratio between the density of natural gas at a defined pressure and temperature, and the density of dry air at the same pressure and temperature. Custody transfer applications rely on real gas characteristics. Ideal gas relative density can be estimated from the respective molar masses of gas and air, but should not be used for custody calculations. Real gas relative density is the term used to refer to the correction for compressibility effects on gases and air. See Appendix A, Calculating Natural Gas Density and the Compressibility of Air, for Air, for additional details and related equations. Specific Gravity is a term similar in meaning to Relative Density. Due to historical reasons, specific gravity is implicitly referenced to 14.73 psia and 60 °F. 2.16 Sensible Heat Sensible heat is potential energy in the form of thermal energy. The magnitude of sensible heat of a thermal body is a product of the body’s mass, its specific heat capacity and its temperature above a reference temperature. 2.17 Therm A therm is a unit of energy equal to 100,000 BtuIT. 2.18 Water Dew Point Upon reduction in the sensible heat of a quantity of gas, the dew point is the temperature at which constituent water vapor begins condensing to the liquid state. The relationship between dew point and molar concentration has been observed and correlated experimentally. The saturability of water in natural gas varies with pressure, temperature and interaction between other constituents, notably CO2 and H2S. 2.19 Water-Saturated and Partially Water-Saturated Gases A water-saturated gas is a gas mixture whose water vapor fraction is in equilibrium with its liquid fraction. The water vapor fraction of a saturated ideal gas mixture is proportional to the ratio of its partial pressure to overall mixture pressure. The partial pressure of the water fraction is equal to the vapor pressure of water at the temperature of interest. For the purpose of this report, a partially water-saturated gas is one whose constituent water vapor is between 7 lbs mass per million standard cubic feet (112 mg/m 3) and saturation. For partially or fully water-saturated natural gases, heating value calculations include compensation for the concentration of water.
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2.20 Wobbe Number (WN), also known as Wobbe Index (WI) Wobbe Number is a measure of the heat rate flowing through an orifice and is a widelyaccepted parameter for estimating and comparing the combustion characteristics of different fuel gases. It is the higher heating value (HHV) of the gas divided by the square root of its real relative density ( RDreal ), both calculated at the same base conditions. The result is dimensionally specified with the unit for heating value.
WN = HHV RDreal
(16)
In common U.S. practice, Wobbe Number is reported in Btu IT per cubic foot at 14.73 psia and 60 °F for dry gas with real relative density at the same reference conditions. In domains using SI units of measure, the Wobbe Number may be reported in MJ per cubic metre at 101.325 kPa and 15 °C for dry gas with real relative density at the same reference conditions.
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3. Basis for Custody Transfer 3.1
Specification of Energy
Where natural gas energy is reported, the unit of measure shall be clearly specified. Upon mutual agreement, the parties involved may report energy in Btu IT , joules or multiples thereof. Therms or dekatherms, effectively, are multiples of the BtuIT and may also be used. In some regions, the kilocalorieIT is used. Users should carefully note the distinction between the kilocalorieIT (1 kcalIT = 4186.8 J) and the kilocalorie(th) (1 kcal(th) = 4184 J). The use of non-conventional natural gas energy units, such as the kilocalorie(th), kilowatt-hour or horsepower-hour, is discouraged. Energy, as opposed to volumetric heating value, is independent of pressure or temperature and may be reported without specified reference conditions. 3.2
Specification of Heating Value
Where natural gas heating value is reported, a complete description shall be provided, including:
• • • •
unit of measure higher versus lower (gross versus net) dry versus saturated reference pressure and temperature
Example 3.2.1 Example 3.2.2 Example 3.2.3
1001.5 BtuIT per cubic foot, Gross, Dry, 14.73 psia and 60 °F 37.30 MJ per cubic metre, Gross, Dry, 101.325 kPa and 15 °C 50.07 MJ per kg, Gross, Dry, 101.325 kPa and 15 °C
For consistency, reference conditions for volumetric heating value must be identical to those used for volume measurement. The assumed combustion reference temperature shall be equal to the reference conditions for volumetric heating value measurement. ` , , `
3.3 Higher (Gross) Versus Lower (Net) Heating Value For custody transfer applications, the reporting basis for heating value measurement shall be Higher (Gross) Heating Value. 3.4
Dry Versus Saturated Heating Value
For custody transfer applications, the reporting basis for heating value measurement shall be Dry Gas Heating Value. Historically, in some domains, volumetric heating value was reported on a water-saturated basis. Theoretical water content was estimated by applying Dalton’s Law of Partial Pressures and the temperature-dependent vapor pressure of water. This arbitrary adjustment was compatible with instrumentation of the time and did not reflect the actual water content of the gas in the pipeline.
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3.5
Energy Derived from Volumetric Measurements
Where the volume of natural gas (at specified pressure and temperature) delivered is known and the gas composition also is known, the energy delivery may be calculated by the following relation: Energy = Volume at Pref , Tref x Volumetric Heating Value at Pref , Tref 3.6
(17)
Energy Derived from Mass Measurements
Where the mass gas is known and the gas composition also is known, energy may be calculated by of thenatural followin following g relation: Energy = Mass x Mass-based Heating Value
(18)
The mass fraction of each constituent in a gas mixture can be determined from the mole fractions and molar masses of each constituent. 3.7
Sampling and Off-line Analysis
Not all all meterin metering g sites sites are equip equipped ped wi with th on-li on-line ne measu measurem rement ent of ga gass prop propert erties ies.. Instead Instead,, sampli sampling ng and calculation strategies may be adequate for providing representativ representativee gas characteristics. characteristics. Many sampling and analysis strategies are possible, such as, but not limited to: • predictive estimates based based on prior-period, time-weig time-weighted hted sampling • retroactive application of flow-weighted sampling • on-line correlative heating value devices, with periodic updates of CO 2 content • on-line chromatographic analysis, normalized with off-line measurements of helium and oxygen • periodic off-site analysis of of spot samples • zone-based calculations based on pipeline hydraulic models The user of a sampling or estimating strategy is accountable for the statistical performance of the strategy. The performance of the strategy must meet the criteria given in section 4 of this report. 3.8
Compressibility Factor
The ideal gas equation applies for very low pressures and very high temperatures where assumptions are valid that the sizes of molecules are negligible relative to the space between molecules and that the molecules do not interact with one another. All compounds and mixtures in the gaseous state exhibit differences between actual pressure, volume, temperature relationships and those predicted by the ideal gas law, particularly at high pressur pres sures es and low tempe temperatu ratures. res. Molecul Molecules es in a real gas are are attra attracted cted to one one another another through through van van der Waal’s forces. Where heating value is stated on a volumetric basis, an adjustment known as the compressibility factor (Z) adjustment is required to correct the ideal gas equation. The compressibility compressibility factor at reference conditions may be obtained by any of the following methods, provi pro vided ded th thee unce uncerta rtain inty ty of the result result is com compat patib ible le wi with th the overa overall ll heatin heating g valu valuee unce uncerta rtaint inty: y: • Calculation of Z using AGA Report No. 8 (2nd Edition) Detail Characterization Method. AGA 8 is the most desired method for gas mixtures whose constituents fall within its range of application.
•
Calculation of Z using summation factors, as described in Appendix A, Calculation of Summations Factors, is Factors, is also acceptable. Note that summation factors may 13
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introduce higher uncertainty, especially for mixtures having the following characteristics:
less than 80 mole% concentration of methane greater than 10 mole% of nitrogen, carbon dioxide or other non-combustible o compounds mixture relative density greater than 0.65 o o
•
Direct measurement of Z with a special apparatus.
•
Inference of Z via correlative methods.
For the pressure and temperature ranges of this report, compressibility factors and summation factors for each compound were approximated using 2 nd virial coefficients coefficients obtained with the NIST REFPROP [1] computer application. Tables and details of the calculations are documented in Appendix A, Tables A.11.1, A.12.1 and A.12.2. 3.9
Enthalpy
The heating value of combustible compounds is affected by the internal energy of reactants and products. Heating value corresponding to one set of contract base conditions will be different from that at another set of conditions. By scientific convention, ‘standard’ enthalpies of formation for compounds are given at 298.15 kelvins (25 °C or 77 °F). Calculations are required to predict enthalpy departure for each reactant and product when the contract base temperature is not equal to 298.15 kelvins.
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Appendix A, Tables A.1.1, A.1.2, A.2.1 and A.2.2 provide pre-calculated heating values with these adjustments built in. Appendix A provides the method used to perform these adjustments. Over the range of contract base conditions supported in this report, the influence of pressure on enthalpy departure is negligible. No adjustments are provided or recommended. 3.10 Accounting for the Presence of Water For custody transfer applications where the water vapor content of the mixture is less than 112 mg/sm3 or 7 lbm/MMscf, the following assumptions are made:
•
The fuel is free of water. Water vapor accompanying combustion air does not influence heating value.
For custody transfer applications where the water content of the mixture is greater than 112 mg/sm3 or 7 lbm/MMscf, the following assum assumptions ptions are made:
• • • •
The fuel contains a water vapor fraction that can be measured by analytical devices or estimated by the dewpoint correlation, given in Appendix A. The concentration of water is included in calculations of heating value. Conforming to the definition of Higher Heating Value, all water vapor produced by combustion or accompanying the pre-burned fuel is condensed in the liquid state. Water vapor accompanying combustion air does not influence heating value.
The primary sensitivity of heating value to water content is an ‘excluded volume’ effect, but other gas properties, including compressibility, compressibility, may be affected.
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Avoid duplicate corrections for water content. If heating value is compensated for water content, there is no need for a separate correction factor (traditionally denoted ‘Fwv’) in gas volume calculations. Note, however, that water vapor should be included in compressibility calculations. The prevailing reference on natural gas water content is IGT Research Bulletin #8 [18]. A number of correlations have been drawn from the tabular data provided by McKetta and Wehe, including that of Kobayashi [16]. The IGT Research Bulletin #8 [18] correlation is included in Appendix A.
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4. Uncertainty 4.1
Acceptance Criteria
The overall uncertainty in energy measurement represents the contributing uncertainties for heating value measurement and flow measurement. The acceptance level for overall energy measurement uncertainty is not specified by this report but should be contractually specified by the parties conducting conducting energy-based transactions. transactions. It is important to understand the complexity of obtaining an accurate determination of heating value. There are numerous causes of increased uncertainty in the determination of the heating value. These include, but are not limited to: • sampling method • sample handling method • analysis method • GC sample inlet system • assignment of gas properties from an analysis of gas at an upstream location on the pipeline hydrocarbons • presence of liquid hydrocarbons • presence of water • calibration error For custody transfer applications, the uncertainty in the heating value determination should be estimated either experimentally or through standard uncertainty calculations, such as described in ANSI/ASME PTC 19.1, NIST 1297 or ISO 5168. If the estimated uncertainty exceeds 0.5% (U95) over a given billing period, and the parties are not satisfied with the level of uncertainty, it is recommended that additional steps be taken to reduce the uncertainty. At a minimum, an audit of procedures, based on current industry standards, should be conducted. If the additional steps are unsuccessful, the uncertainty is considered optimal and no additional steps are recommended. If estimating uncertainty via in-situ testing, a calibration gas or other portable standard, whose heating value uncertainty is less than 0.2% (U95) and traceable to a national standard, should be used as the reference.
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5. Heating Value Determination Methods 5.1
Heating Value from Gas Composition
5.1.1 General Requirements The methods listed below share the following assumptions:
•
Each constituent of interest can be quantified.
• •
The properties of each constituent, including heating value, are known. The compressibility of the mixture can be determined if volumetric heating value is required.
The measurement uncertainty arising from these methods comes from:
• • • • •
the gas sampling system repeatability of the detectors and other physical constituents sensitivity to ambient conditions uncertainty of calibration gas(es) purity of the carrier gas
5.1.2 Gas Chromatography Chromatography is a process of separation by adsorption. Following separation, the constituents of a mixture are quantified using special sensors. In typical implementations, a chromatograph has two main constituents: a control unit and an analyzer unit. The analyzer unit contains physical apparatus for separating and detecting the presen pre sence ce of of compo compound unds. s. The The con contro troll u unit nit seque sequence ncess tthe he oper operati ation on of tthe he analyz analyzer, er, qua quanti ntifie fiess the the gas constituents and performs calculations based on the measurements. Chromatograph performance is dependent on calibration, involving reference gas mixtures of known characteristics. Calculation bias is avoided by ensuring that configurable gas property tables and calculations are set appropriately for the intended base conditions. 5.1.3 Mass Mass Spectrometry Spectrometry The basis for mass spectrometry is the use of electromagnetic energy to separate and quantify gas constituents, according to their molecular mass. This method is characterized by its high speed of analysis. However, it is unable to distinguish compound isomers, such as normal butane and isobutane. A user of this technology must provide additional information about the proportions of isomers to obtain natural gas heating values with acceptable uncertainty. 5.2
Heating Value Measurement
5.2.1 General Requirements Direct measurement of heating value involves burning sample gas in controlled conditions and measuring the bulk heat produced. Depending on the implementation, heat measurement may occur directly in the flame or in media exposed to the flame. 5.2.2 Calorimeter Once the primary means of obtaining heating value data, relatively few calorimeters remain in service at field locations. The operational basis for most field calorimeters 17 ` , ,
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devices is ‘differential temperature’. That is, the difference in temperature between air exposed to a heated surface versus its temperature prior to to exposure. The uncertainty of this technology is driven by equipment repeatability, the stability of ambient conditions, water purity and calibration gas quality. 5.2.3 Fuel/Air Fuel/Air Titration Titration Titration exploits the relationship between stoichiometric air/fuel ratio and heating value. One or more calibration gas is used to define air/fuel ratio for known heating value, after which the analyzer infers measured air/fuel ratios. Measurement uncertainty is dependent on heating strength value of the from correlation between heating value and carbon number as well as the factors listed in section 5.1.1. 5.3
Heating Value from Inferential (Correlative) Methods
Inferential techniques for characterizing the heating value of natural gas do not require a detailed composition assay. Natural gas is composed largely of paraffin hydrocarbons having properties that are inter-dependent inter-dependent because of similar molecular structure. Inferential methods methods make use of this inter-dependence to characterize the hydrocarbon energy without performing a detailed composition assay. Inferential techniques are relatively simple, typically requiring measurements or calculations of the diluent concentrations (predominantly nitrogen and carbon dioxide) and one or more thermodynamic and/or transport properties such as speed of sound, viscosity, viscosity, thermal conductivity, conductivity, pressure pressure and temperature. temperature. Inferential methods can provide cost savings over the traditional gas chromatograph installation and near real-time gas property determination at locations where spot or composite sample analyses traditionally are used. There is precedence for inferential characterization of natural gas properties. The Gross Characterization Method described in AGA Report No. 8 is an equation of state for calculating natural gas density (compressibility factor), where the composition is characterized by one of two methods. The first method assumes that volumetric gross heating value, relative density (specific gravity), and carbon dioxide concentration are known. The second assumes that relative density (specific gravity), carbon dioxide concentration and nitrogen concentration are known. Although the Gross Characterization Method addresses the determination of gas density (compressibility factor) only, the general characterization approach may be applied to other gas properties required for energy measurement, such as heating value. An example of this type of inferential characterization of natural gas properties uses least square regressions of a database of known gases, along with known values of sound speed, carbon dioxide concentration and nitrogen concentration, to determine the density, molecular weight and heating value of an unknown gas. Other examples of inferential methods available involve using the sensitivity of properties to changes in composition to infer gas properties and comparing measured properties of one or more reference gases, in combination with measured properties of the unknown gas to infer gas properties. Although this is a relatively new technology, it is considered to be fundamentally sound and capable of providing accuracies acceptable for custody transfer measurement.
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6. References
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[1]
E. W. Lemmon, M. L. Huber and M. O. McLinden, "REFPROP, NIST Standard Reference Database 23, Version 8.0,” Physical and Chemical Properties Division, National Institute Institute of Standards and Tec Technology. hnology.
[2]
B. J. Caldwell, “Fuel Gas Energy Metering,” American Gas Association Transmission Measurement Committee Committee Report No. 5, 1981.
[3]
A. E. Humphreys, “GERG Technical Monograph TPC/1 (1986) – Some Thermophysical Constants of Components of Natural Gas and Cognate Fluids,” Groupe Europeen De Recherches Gazieres (GERG), 1986.
[4]
GPA, “GPA Standard 2172-96 – Calculation of Gross Heating Value, Relative Density and Compressibility Factor for Natural Gas Mixtures from Compositional Analysis,” Gas Processors Association, 1996.
[5] [5 ]
GPA, “GPA Standard 2145-03 – Table of Physical Constants of Paraffin Hydrocarbons and Other Components of Natural Gas,” Rev. 2, Gas Processors Association, 2003.
[6]
ISO, “ISO/DIS 6976:1995 Natural Gas – Calculatio Calculation n of Calorific Values, Density, Relative Density and Wobbe Index from Composition”, International Organization for Standardization.
[7]
K.E. Starling and J.L. Savidge, “Compressibility “Compressibility Factors of Natural Gas and Other Related Hydrocarbon Gases,” American Gas Association Transmission Measurement
[8]
Committee Report No. 8, Second Edition, Second Printing, July, 1994. ASTM, “D3588-98(2003) Standard Practice for Calculating Heat Value, Compressibility Factor and Relative Density of Gaseous Fuels,” American Society of Testing and Materials, Subcommittee D03.
[9]
B. E. Poling, J. M. Prausnitz and J. P. O’Connell, “The Properties of Gases and Liquids,” Fifth Edition (New York: McGraw-Hill, 2000).
[10]
ISO, “Guide to the Expression of Uncertainty in Measurement” (GUM), First Edition 1993, corrected and reprinted 1995, International Organization for Standardization, Genéve, Switzerland, 1978.
[11]
D. L. George and E. Kelner, “Uncertainties “Uncertainties in Natural Gas Properties Determined by Gas Chromatography,” Southwest Research Institute, 2006.
[12]] [12
J.D. Cox, D.D. Wagman and V.A. Medvedev, “CODATA Key Values for Thermodynamics,” Thermodynamics,”
[13]
Committee on Data for Science and Technology (CODATA), 2006. J. W W.. Ste Stewart wart and L. S. Traweek, “Definition of Btu in the U.S. Natural Natural Gas Industry: An Update,” Engineering Technical Technical Note M-92-2-1, American Gas Association, April 1992.
[14]
ASTM, “D1826-77 (1977) Test Method for Calorific Value of Natural Gas Ranges by Continuous Recording Calorimeter,” American Society of Testing and Materials.
[15]
D. Hyams, “CurveExpert, A Curve Fitting System for Windows,” Version 1.37.
[16]
R. Kobayashi, K. Y. Song, and E.D. Sloan, “Phase Behaviour of Water/Hydrocarbon Water/Hydrocarbon Systems” in H. B. Bradley, (ed.), Petroleum Engineering Handbook , Society of Petroleum Engineers, Richardson, TX, 1987.
[17]
GPA, GP GPA A Research Research Bulletin Bulletin RB 181-86 – “Heating “Heating Value – Basis Basis for Custody Transfer,” Gas Processors Association, 1986.
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[18]
Bukacek, R.F., “Equilibrium Moisture Content of Natural Gases,” Research Bulletin #8, Institute of Gas Technology (IGT), Chicago, USA, 1955.
[19]
J. Kubes Kubesh, h, S.R. King & W.E. Liss, “Effect of Gas C Composition omposition on Octane Number of Natyural Gas Fuels,” Document Document # 922359, SAE Intern International, ational, 1992.
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APPENDIX A
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A–1 Copyright American Gas Association
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Pre-Calculated Tables of Ideal Gas Gross Heating Value (Volumetric Basis) Table A.1.1 - Ideal Gas Gross Heating Value (Volumetric Basis) - Imperial Units of Measure Ideal Gas Gas Gros s Heating Value in BTU(IT) per Cubic Foot temperature base pressure base Methane Ethane
60 °F 14.4 p ps sia
60 °F 14.65 p ps sia
59 °F 14.696 p ps sia
60 °F 14.696 p ps sia
60 °F 14.73 p ps sia
60 °F 15.025 p ps sia
989.6 1734.0
1006.8 1764.1
1012.0 1773.2
1010.0 1769.7
1012.3 1773.8
1032.6 1809.3
Propane Isobutane Normal Butane Isopentane Normal Pentane Hexane Heptane Octane Nonane Decane Hydrogen Sulphid Sulphid e Water Hydrogen Carbon Ca rbon Monox ide
2465.5 3186.5 3196.7 3920.3 3928.0 4660.3 5391.7 6123.0 6855.5 7587.1 624.3 49.3 317.6 314.1
2508.3 3241.8 3252.2 3988.4 3996.2 4741.2 5485.3 6229.3 6974.5 7718.8 635.1 50.2 323.1 319.5
2521.1 3258.4 3268.8 4008.8 4016.7 4765.4 5513.4 6261.2 7010.2 7758.3 638.4 50.4 324.8 321.1
2516.2 3252.0 3262.4 4000.9 4008.8 4756.1 5502.5 6248.9 6996.4 7743.0 637.1 50.3 324.2 320.5
2522.0 3259.5 3269.9 4010.2 4018.0 4767.1 5515.3 6263.4 7012.6 7760.9 638.6 50.4 324.9 321.3
2572.5 3324.8 3335.4 4090.5 4098.5 4862.5 5625.7 6388.8 7153.0 7916.4 651.4 51.4 331.4 327.7
Ethylene Propylene 2,2-Dimethyl 2,2 -Dimethyl Prop ane 2-Methyl 2-M ethyl Pentane 3-Methyl 3-M ethyl Pentane 2,2-Dimethyl Butane 2,3-Dimethyl Butane Methyl Me thyl Alcoho l
1 25 26 87 6..5 5 3904.5 4652.1 4654.6 4639.5 4648.2 849.3
1 25 39 24 6..7 2 3972.3 4732.8 4735.4 4720.1 4728.9 864.1
1 26 30 32 8..9 1 3992.6 4757.0 4759.7 4744.2 4753.1 868.5
1 25 39 39 3..7 5 3984.8 4747.7 4750.3 4734.9 4743.7 866.8
1 26 30 33 8..4 9 3994.0 4758.7 4761.3 4745.8 4754.7 868.8
1 26 33 85 5..5 8 4074.0 4854.0 4856.7 4840.9 4850.0 886.2
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Table A.1.2 - Ideal Gas Gross Heating Value (Volumetric Basis) - SI Units of Measure Ideal Gas Gross Heating Value in Megajoules per Cubic Meter temperature base pressure base Methane
0 °C
15 °C
20 °C
100 kPa
101.325 kPa
98.0665 kPa
39.318
37.706
35.852
Ethane Propane Isobutane Normal Butane Isopentane Normal Pentane Hexane Heptane Octane Nonane Decane Hydrogen Sulphide Water Hydrogen
68.879 97.925 126.555 126.958 155.695 1 55.998 15 185.074 214.118 243.157 272.241 301.291 24.787 1.985 12.621
66.066 93.935 121.405 121.793 149.364 149.657 177.554 205.422 233.285 261.191 289.064 23.784 1.879 12.102
62.822 89.324 115.449 115.818 142.038 142.317 168.847 195.350 221.848 248.385 274.893 22.619 1.779 11.506
Carbon Monoxide Ethylene Propylene 2,2-Dimethyl Propane 2-Methyl Pentane 3-Methyl Pentane 2,2-Dimethyl Butane 2,3-Dimethyl Butane Methyl Alcohol
12.452 62.239 90.791 155.067 184.749 18 184.853 18 184.252 184.599 33.758
11.965 59.721 87.116 148.762 177.242 177.340 176.764 177.095 32.361
11.384 56.795 82.848 141.465 168.550 168.643 168.095 168.410 30.766
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A–3
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Pre-Calculated Tables of Ideal Gas Gross Heating Value (Mass Basis) Table A.2.1 Ideal Gas Gross Heating Value (Mass Basis) - Imperial Units of Measure Ideal Gas Gas Gross HV in BTU(IT) per Pound Methane Ethane
Propane Isobutane Normal Butane Isopentane Normal Pentane Hexane Heptane Octane Nonane Decane Hydrogen Sulphide Water Hydrogen Carbon Monoxide Ethylene Propylene 2,2-Dimethyl Propane 2-Methyl Pentane 3-Methyl Pentane 2,2-Dimethyl Butane 2,3-Dimethyl Butane Methyl Alcohol
59 °F 23892 3892.7 .7 22335 2335.0 .0
60 °F 23 2389 891 1.3 2 22 233 333 3.8
21654 1654.5 .5 21233 1233.5 .5 21301 1301.4 .4 21044 1044.7 .7 21086 1086.0 .0 20944 0944.7 .7 20840 0840.0 .0 20760 0760.6 .6 20701 0701.9 .9 20652 0652.5 .5 7094.3 70 1060.4 61025 1025.6 .6 4342.4 21640 1640.6 .6 21045 1045.0 .0 20959 209 59.8 .8 20907 0907.6 .6 20919 0919.2 .2 20851. 2085 1.3 3 20890. 2089 0.3 3 10266 0266.6 .6
21 2165 653 3.5 21 2123 232 2.5 21 2130 300 0.4 21 2104 043 3.8 21 2108 085 5.1 20 2094 943 3.8 20 2083 839 9.1 2 20 075 759 9.7 20 2070 701 1.0 20 2065 651 1.6 7094.0 1059.8 61 6102 021 1.9 4342.5 21 2163 639 9.8 21 2104 044 4.2 20 2095 958 8.9 20 2090 906 6.7 20 2091 918 8.3 20 2085 850 0.3 20 2088 889 9.4 10 1026 265 5.9
A–4
` , , ` , ` , , ` , , ` ` ` ` ` ` , , , , ` ` ` , , ` -
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Table A.2.2 Ideal Gas Gross Heating Value (Mass Basis) - SI Units of Measure Ideall Gas Gross HV in MJ per Kilo gram Idea 0 °C Methane 55.661 Ethane 52.024 Propane 50.434 Isobutane 49.451 Normal Butane 49.608 Isopentane 49.010 Normal Pentane 49.105 49 Hexane 48.775 Heptane 48.530 Octane 48.345 Nonane 48.207 Decane 48.092 Hydrogen Sulphide 16.517 Water 2.502 Hydrogen 142.183 Carbon Monoxide 10.096 Ethylene 50.386 Propylene 49.001 2,2-Dimethyl Propane 48.812 2-Methyl Pentane 48.689 3-Methyl Pentane 48.716 2,2-Dimethyl Butane 48.558 2,3-Dimethyl Butane 48.649 Methyl Alcohol 23.927
A–5
15 °C 55.574 51.951 50.368 49.389 49.547 48.950 49.046 48.717 48.474 48.289 48.153 48.038 16.501 2.466 141.946 10.100 50.336 48.951 48.753 48.631 48.658 48.500 48.591 23.880
20 °C 55.545 51.927 50.347 49.369 49.527 48.930 49.026 48.698 48.455 48.271 48.134 48.020 16.496 2.455 141.867 10.102 50.319 48.934 48.733 48.612 48.639 48.481 48.572 23.865
` , , ` , ` , , ` , , ` ` ` ` ` ` , , , , ` ` ` , , ` -
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Not for Resale
N P C r o o o r v p e i y d r p e i r d g o h d b t u y A c m t I i H e o n S r i o u c r n a n d n e e G t r w c l a s i o A r k e n s i s n s g e o p w c i e i a t t r i m h o i A n t t G e d A w i t h o u t l i c e n s e f r o m I H S
` , , ` ` ` , , , , ` ` ` ` ` ` , , ` , , ` , ` , , ` -
Table A.3.2 Calculation Results
Calculation Calculation Re Result sult s Compressibility Factor (Z) at Pb, Tb Gross HV at Pb, Tb Net HV at Pb, Tb Wobbe Number Ideal Gas Relative Density Real Gas Relative Density MON 1 (Linear Method) MON 2 (CARB Method)
N o t f o r R e s a l e
Methane Methane Number Number (via (via MON MON 1 2 method) method) Gas Constant Standard T for Hf and Cp Heat of Vaporization of Water delta H for Liquid Water Ideal Gas Molar Volume at Pb, Tb Molar Mass of Air Compressibility Factor (Z) of Air at Pb, Tb
0.997776 1034.8
B TU(IT)/ft
3
corrected correcte d f or compress compressibility ibility
933.6
B TU(IT)/ft
3
corrected correcte d f or compress compressibility ibility
B TU(IT)/ft
3
corrected correcte d f or compress compressibility ibility
1326.5 0.6075 0.6086 127.4 124.7 87.8 83.5 8.314472 298.15 44.41 -711.1 23.6357 28.9625 0.999566
c o r r ec t ed f o r c o m p r es s i b i l i t y
-1
-1
J mol K K el v i n s k J /m o l e at k J /m o l e at l i t r es
60 60
°F °F
A–7
N P C r o o o r v p e i y d r p e i r d g o h d b t u y A c m t i I H e o n S r i c o u a r n n n d e e G t a w r l s i o c r e A k n s i s n s g e o p w c i e i a r t i h t m o i A n t t G e d A w i t h o u t l i c e n s
Example Calculation of Volumetric Heating Value (SI Units) Table A.4.1 Input Data and Intermediate Calculation Results
e f r o m I H S
AGA 5 Calcu lati on Sp readsh eet - SI Unit s of Measure
` , , ` ` ` , , , , ` ` ` ` ` ` , , ` , , ` , ` , , ` -
N o t f o r R e s a l e
mole fraction (xi )
molar mass
molar mass * xi
Methane Nitrogen Carbon Dioxide Ethane Propane Water (gas) Hydrogen Sulfide Hydrogen Carbon Monoxide Oxygen Isobutane Normal Butane Isopentane Normal Pentane Hexane Heptane Octane Nonane Decane Helium
0.906724 0.031284 0.004676 0.045279 0.008280 0.000000 0.000000 0.000000 0.000000 0.000000 0.001037 0.001563 0.000321 0.000443 0.000393 0.000000 0.000000 0.000000 0.000000 0.000000
16.0425 28.0134 44.0095 30.0690 44.0956 18.0153 34.0809 2.0159 28.0101 31.9988 58.1222 58.1222 72.1488 72.1488 86.1754 100.2019 114.2285 128.2551 142.2817 4.0026
14.5461 0.8764 0.2058 1.3615 0.3651 0.0000 0.0000 0.0000 0.0000 0.0000 0.0603 0.0908 0.0232 0.0320 0.0339 0 .0000 0 .0000 0 .0000 0 .0000 0.0000
Argon 2,2-Dimethyl Propane 2-Methyl Pentane 3-Methyl Pentane 2,2-Dimethyl Butane 2,3-Dimethyl Butane Ethylene Propylene Methyl Alcohol
0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000
39.9480 72.1488 86.1764 86.1764 86.1764 86.1764 28.0532 42.0797 32.0419
0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
1.000000
Pressure Base (Pb) Temperature Base (Tb)
v er s i o n 1.1 Gross Ideal Ideal HV (MJ/m )
26- Feb - 08 Gross HV * x i
Net Ideal Ideal HV (MJ/m )
Net HV * x i
Summation factor (s)
Summation factor * x i
37.706 0.000 0.000 66.067 93.936 1.879 23.784 12.102 11.965 0.000 121.404 121.792 149.363 149.656 177.554 205.422 233.286 261.191 289.065 0.000
34.1893 0.0000 0.0000 2.9914 0.7778 0.0000 0.0000 0.0000 0.0000 0.0000 0.1259 0.1904 0.0479 0.0663 0.0698 0.0000 0.0000 0.0000 0.0000 0.0000
33.948 0.000 0.000 60.429 86.419 0.000 21.905 10.223 11.965 0.000 112.008 112.396 138.088 138.381 164.400 190.389 216.373 242.399 268.394 0.000
30.7815 0.0000 0.0000 2.7362 0.7155 0.0000 0.0000 0.0000 0.0000 0.0000 0.1162 0.1757 0.0443 0.0613 0.0646 0.0000 0.0000 0.0000 0.0000 0.0000
0.044527 0.017122 0.075006 0.091608 0.133321 0.251281 0.091952 0.024621 0.021735 0.027640 0.169523 0.180657 0.221387 0.233047 0.298395 0.365975 0.434264 0.502845 0.599127 0.022005
0.040374003 0.000535638 0.000350728 0.004147915 0.001103899 0 0 0 0 0 0.000175796 0.000282367 7.10653E-05 0.00010324 0.000117269 0 0 0 0 0
0.000 148.762 177.242 177.340 176.764 177.095 59.721 87.116 32.361
0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
0.000 137.487 164.088 164.186 163.610 163.941 55.962 81.478 28.602
0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
0.027340 0.199644 0.280515 0.291390 0.267848 0.280955 0.079756 0.125852 0.295020
0 0 0 0 0 0 0 0 0
17.5950
38.4588
101.325 15
34.69528
kPa °C
A–8
N P C r o o o r v p e i y d r p e i o r d t g h h d b A u y c m t i I H e o n S r i c o u a r n n d n e e G t a w r l s i o c r e A k n s i s n s g e o p w c i e i a r t h t i m o i A n t t G e d A w i t h o u t l i c e n s e f r o m I H S
` , , ` , ` , , ` , , ` ` ` ` ` ` , , , , ` ` ` , , ` -
Table A.4.2 Calculation Results
Calculation Calculation Re Result sult s Compressibility Factor (Z) at Pb, Tb Gross HV at Pb, Tb Net HV at Pb, Tb Wobbe Number
0.997766 38.545 34.773 49.408
3
MJ/m 3 MJ/m 3 MJ/m
corrected f or compress corrected compressibility ibility corrected correcte d f or compress compressibility ibility corrected correcte d f or compress compressibility ibility
0.04726
N o t f o r R e s a l e
Ideal Gas Relative Density Real Gas Relative Density MON 1 (Linear Method) MON 2 (CARB Method) Methane Number (via MON 1 method) Methane Number (via MON 2 method) Gas Constant Standard T for Hf and Cp Heat of Vaporization of Water delta H for Liquid Water Ideal Gas Molar Volume at Pb, Tb Molar Mass of Air Compressibility Factor (Z) of Air at Pb, Tb
0.60751 0.60860 127.4 124.7 87.8 83.5 8.314472 298.15 44.433 -752.9 23.6449 28.9625 0.999561
c o r r ec t ed f o r c o m p r es s i b i l i t y
-1
-1
J mol K K el v i n s k J /m o l e at k J /m o l e at l i t r es
15 15
A–9
Standard Enthalpies of Formation Table A.5.1
` , , ` ` ` , , , , ` ` ` ` ` ` , , ` , , ` , ` , , ` -
Enthalpies of Formation at 298 298.15 .15 kelvins kJ/mole Methane -74.54 Nitrogen 0 Carbon Dioxide -393.51 Ethane -83.82 Propane -104.68 W ater (gas) -241.814 Hydrogen Sulfide -20.63 Hydrogen 0 Carbon Monoxide -110.53 Oxygen 0 Isobutane -134.99 Normal Butane -125.79 Isopentane -153.7 Normal Pentane -146.76 Hexane -166.92 Heptane -187.78 Octane -208.75 Nonane -228.74 Decane -249.46 Helium 0 Argon 0 2,2 ,2-D -Diime meth thy yl Pro ropa pane ne -1 -167 67..9 2-Methyl Pentane -174.3 3-Methyl Pentane -172 2,2-D -Diime metthyl Butane -185.6 2,3-D -Diime metthyl Butane -177.8 Ethylene 52.47 Propylene 20.41
°C °C
M eltfhuyrl D Ailocxoihdoel Su
-2-9260.181
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Stoichiometric Coefficients Table A.6.1
Methane Nitrogen Carbon Dioxide Ethane Propane Water (gas) Hydrogen Sulfide Hydrogen Carbon Monoxide Oxygen Isobutane Normal Butane Isopentane Normal Pentane Hexane Heptane Octane Nonane Decane Helium Argon 2,2-Dimethyl Propane 2-Methyl Pentane 3-Methyl Pentane 2,2-Dimethyl Butane 2,3-Dimethyl Butane Ethylene Propylene
Stoichiometric Coefficients Ox y g en Wat er -2 2
Car b o n Di o x i d e 1
Su l f u r Di o x i d e 0
-3.5 -5
3 4
2 3
0 0
-1.5 -0.5 -0.5
1 1 0
0 0 1
1 0 0
-6.5 -6.5
5 5
4 4
0 0
-8 -8 -9.5 -11 -12.5 -14 -15.5
6 6 7 8 9 10 11
5 5 6 7 8 9 10
0 0 0 0 0 0 0
-8 -9.5 -9.5 -9.5 -9.5 -3 -4.5
6 7 7 7 7 2 3
5 6 6 6 6 2 3
0 0 0 0 0 0 0
M ethyl Dioxide Alcohol Sulfur
-1.5
2
1
0
A – 11 --`,,```,,,,````-`-`,,`,,`,`,,`---
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Balanced Combustion Reaction Equations for Common Hydrocarbons Table A.7.1 Methane
1 CH4
+
2 O2
⇒
1 CO2 +
2 H2O
Ethane
2 C2H6
+
7 O2
⇒
4 CO2 +
6 H2O
Propane
1 C3H8
+
5 O2
⇒
3 CO2 +
4 H2O
Butane
2 C4H10 +
13 O 2
⇒
8 CO2 +
10 H2O
Pentane
1 C5H12 +
8 O2
⇒
5 CO2 +
6 H2O
Hexane
2 C6H14 +
19 O 2
⇒
12 CO 2 +
14 H2O
Heptane
1 C7H16 +
11 O 2
⇒
7 CO2 +
8 H2O
Octane
2 C8H18 +
25 O 2
⇒
16 CO 2 +
18 H2O
Nonane
1 C9H20 + 2 C10H22 +
14 O 2 31 O 2
⇒
⇒
9 CO2 + 20 CO 2 +
10 H2O 22 H2O
Decane
Ideal Gas Molar Heating Values at 298.15 K Table A.8.1
Methane Nitrogen Carbon Dioxide Ethane Propane W ater (gas) Hydrogen Sulfide
Ideal Gas Gas Molar Heating Value (kJ/mole) Gr Gross oss HV HV a att 29 298. 8.15 15 K Net Net HV at 298 298.1 .15 5K 890.63 802.60 0.00 0.00 0.00 0.00 1560.69 1428.64 2219.17 2043.11 44.016 0.00 562.01 517.99
Hydrogen Carbon Monoxide Oxygen Isobutane Normal Butane Isopentane Normal Pentane Hexane Heptane Octane Nonane Decane Helium Argon
285.83 282.98 0.00 2868.20 2877.40 3528.83 3535.77 4194.95 4853.43 5511.80 6171.15 6829.77 0.00 0.00
241.81 282.98 0.00 2648.12 2657.32 3264.73 3271.67 3886.84 4501.30 5115.66 5730.99 6345.59 0.00 0.00
2,2-Dimethyl Propane 2-Methyl Pentane 3-Methyl Pentane 2,2-Dimethyl Butane 2,3-Dimethyl Butane Ethylene Propylene Methyl Alcohol
3514.63 4187.57 4189.87 4176.27 4184.07 1411.15 2058.43 764.17
3250.53 3879.46 3881.76 3868.16 3875.96 1323.12 1926.38 676.14
A – 12 --`,,```,,,,````-`-`,,`,,`,`,,`---
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Enthalpy of Vaporization of Water Energy is released when a quantity of fluid in the gas state is condensed to the liquid state. By definition, the Gross heating value of natural gas includes the heat released when the water produced by combustion is condensed. At the reference condition of 298.15 kelvins (77 °F), the enthalpy of vaporization of water is approximately 44.016 kJ per mole. A theoretical case exists where water vapor is a constituent of the unburned fuel stream and condensed to a liquid following combustion. For the purpose of this report, it is assumed that water vapor accompanying fuel contributes its enthalpy of vaporization to the fuel mixture gross heating value. The enthalpy of vaporization of water varies with temperature. The calculations in this report incorporate a simple interpolation of data presented by Humphreys [3]. For T
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